Kinetic studies on the mechanism of the nitraminopyridine rearrangement

Abstract

Rate data are reported for the rearrangement, in 92% sulfuric acid at 30º, of a series of 4-X-2-nitra-minopyridines (X = H, Me, Br, CI, MeO, CO₂H) and of 4-methyl-2-nitramino(3-D)pyridine. Values of pK_a for second protonation of the corresponding pyridin-2-amines were also measured and rate constants for nitration of the monoprotonated pyridinamines were thereby calculated. The results suggest that the rate-determining step occurs prior to formation of the appropriate 3-and 5-nitro σ complexes. The nature of this step is not clear, however, and a key role for the nitramine itself is not proven by the current evidence.